(1) Field of the Invention
The present invention relates to motion conversion devices that convert rotary motion into linear motion or torque into pulling force and vice versa. The term linear motion applies throughout the present invention for straight motion, arc motion, partially circular or any arbitrary curved motion that is generated by pulling force. The invented motion conversion device can be used in robotics, welfare, medical equipment, or in general as actuator mechanism for conversion between rotary and linear motion or conversion between torque and pulling force.
(2) Description of Related Art
For robots, medical equipment, prostheses and similar it is required to provide small size power source that produces high pulling force with high efficiency, high conversion ratio, high force amplification ratio, and additionally is of low-cost, lightweight, and has noiseless operation.
The known mechanisms to convert rotation into linear motion are composed of rack and pinion, belts and pulleys, ball and screw, or various linkage mechanisms. In the field of robotics electrical motors are used combined with gear reducers to amplify the torque. Due to low mechanical efficiency and high friction in the gears, free motion of such mechanisms is difficult to achieve.
An example of a joint driving means of robots and other mechanisms is shown in FIG. 13, where the rotational axis of rotary motion source (motor 1 and gear 2) and axis of the joint are aligned, and the motor 1 is attached at one side of the link 7, which results in poor balance and bad aesthetic impression.
Configurations as shown in FIG. 14, where the motor 1 and the gear 2 are aligned with the arm 7 so that the axis of joint 6 is perpendicular to the axis of motor 1 and gear 2, are also used. In such configuration the rotary motion of motor 1 is transmitted to the joint 6 through the gear 2 and orthogonal bevel gear 3. The mechanism appears compact but is more complex due to additional bevel gear which in total results in higher costs, more weight, and more backlash in the system.
Mechanisms shown in FIG. 15, where motor 1, gear 2, and pulley 4 are positioned at some distance away from the joint 6, and the wire 5 that is fixed to the pulley 4 is driving the joint 6 are also frequently used. In such mechanism the rotary motion of motor 1 is through the gear 2 and pulley 4 converted into linear motion of wire 5, and the linear motion of wire is used to drive the joint 6.